don't get this?
what audio device have you chosen in Audio Devices for the zone you are playback from ? (or the default zone Player if you have not set up Zones)
what playback device is showing in Windows?
Normally you would want the TV just as a monitor, so you would not be choosing it as the audio device (although the TV might show up as an option). You would want either your sound card, or external DAC to do the conversion ... not the TV of course. If the AV receiver has the DAC incorporated in it there are can be multiple options to set it up, I don't know what you have.
I'm assuming you have HDMI from a Sound Card to an AV receiver for muti-channel playback? If not a SPDIF output might be easier.
Have you read this and browsed any relevant links at the bottom of the page ?
http://wiki.jriver.com/index.php/Audio_Setup. You might want to do that and check your basic configuration.
You are right though HDMI can be a bit dodgy sometimes if not set up right. Might be a good idea to indicate you entire signal chain including external DAC; how many playback channels, tuners on your PC; if your receiver is a pre/pro etc. if you still have issues after rechecking the WIki.
PS - you might want to try Theater View rather than just Display view for music ... display view is a bit limiting, and you can control everything form the TV screen that way.